Increasing cost of fossil fuel and environmental concerns have stimulated worldwide interest in developing alternatives to petroleum-based fuels, chemicals, and other products. Biomass (material derived from living or recently living biological materials) is one category of possible renewable alternative to such fuels and chemicals.
A key challenge for promoting and sustaining the use of biomass in the industrial sector is the need to develop efficient and environmentally benign technologies for converting biomass to useful products. A number of biomass conversion technologies unfortunately tend to carry additional costs which make it difficult to compete with products produced through the use of traditional resources, such as fossil fuels. Such costs often include capital expenditures on equipment and processing systems capable of sustaining extreme temperatures and high pressures, and the necessary operating costs of heating fuels and reaction products, such as fermentation organisms, enzymatic materials, catalysts, and other reaction chemicals.
One promising technology is the BioForming® platform being developed by Virent, Inc. The BioForming platform is based on the combination of aqueous phase reforming (APR) and/or hydrodeoxygenation (HDO) with conventional catalytic processing technologies, including acid condensation, base catalyzed condensation, acid catalyzed dehydration, and/or alkylation. In its operation, soluble carbohydrates extracted from biomass are introduced into a BioForming reactor with water as an aqueous feedstock. The aqueous carbohydrate feedstock is then converted into reactive intermediates through one or more APR/hydrodeoxygenation reactions. Once formed, the chemical intermediates undergo further catalytic processing to generate hydrocarbons for gasoline, jet fuel, diesel, or chemicals. Other aspects of the BioForming process are described in U.S. Pat. Nos. 6,699,457; 6,964,757; 6,964,758; and 7,618,612 (all to Cortright et al., and entitled “Low-Temperature Hydrogen Production from Oxygenated Hydrocarbons”); U.S. Pat. No. 6,953,873 (to Cortright et al., and entitled “Low-Temperature Hydrocarbon Production from Oxygenated Hydrocarbons”); U.S. Pat. Nos. 7,767,867; 7,989,664; and 8,198,486 (all to Cortright, and entitled “Methods and Systems for Generating Polyols”); U.S. Pat. Nos. 8,053,615; 8,017,818; and 7,977,517 and U.S. Patent Application Pub. Nos. 2011/0257448; 2011/0245543; 2011/0257416; and 2011/0245542 (all to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); U.S. Pat. No. 8,231,857 (to Cortright, and entitled “Catalysts and Methods for Reforming Oxygenated Compounds”); U.S. Patent Application Ser. No. 2010/0076233 (to Cortright et al., and entitled “Synthesis of Liquid Fuels from Biomass”); International Patent Application No. PCT/US2008/056330 (to Cortright and Blommel, and entitled “Synthesis of Liquid Fuels and Chemicals from Oxygenated Hydrocarbons”); and commonly owned co-pending International Patent Application No. PCT/US2006/048030 (to Cortright et al., and entitled “Catalyst and Methods for Reforming Oxygenated Compounds”), all of which are incorporated herein by reference.
One key step in the BioForming process is the ability to convert carbohydrates at moderate temperatures and pressures to produce intermediate compounds for further processing or use in industry. To be commercially effective, however, the process must be able to convert the carbohydrate feedstock to the necessary compounds at yields that are economical as compared to other technologies. The process must also effectively remove oxygen from the carbohydrate without a significant disruption of the corresponding carbon backbone.
Work has been done to allow the hydrogen generated during APR to be used in downstream processing of biomass and biomass-derived feedstocks to generate oxygenated hydrocarbons. Depending on current market conditions (such as the relative cost of biomass-derived feedstocks and other hydrogen sources), it can also be economically advantageous to supply external hydrogen. However, using external hydrogen can saturate the biomass feedstock such that it is completely deoxygenated into alkanes. Therefore, improved catalysts that are selective to avoid or minimize alkane generation while also maximizing mono- and polyoxygenate production in the presence of external hydrogen would be beneficial.
Researchers have recently developed methods to react pure hydrogen with sugars (xylose and glucose) and sugar alcohols (glycerol, xylitol, and sorbitol) over hydrogenation and hydrogenolysis catalytic materials to generate lower molecular weight compounds. For instance, U.S. Pat. Nos. 6,841,085; 6,677,385; and 6,479,713 to Werpy et al., disclose methods for the hydrogenolysis of both carbon-oxygen and carbon-carbon bonds in 5 and 6 carbon sugars using a rhenium (Re)-containing multimetallic catalyst to produce products, such as propylene glycol (PG). The Re-containing catalyst may also include Ni, Pd, Ru, Co, Ag, Au, Rh, Pt, Ir, Os and Cu. The conversion takes place at temperatures in a range from 140° C. to 250° C., and more preferably 170° C. to 220° C., and a hydrogen pressure between 600 psi to 1600 psi hydrogen.
Dasari et al. also disclose hydrogenolysis of glycerol to PG in the presence of hydrogen from an external source, at temperatures in a range from 150° C. to 260° C. and a hydrogen pressure of 200 psi, over Ni, Pd, Pt, Cu, and Cu-chromite catalysts. The authors reported increased yields of propylene glycol with decreasing water concentrations, and decreasing PG selectivity at temperatures above 200° C. and hydrogen pressures of 200 psi. The authors further reported that Ni, Ru, and Pd were not very effective for hydrogenating glycerol. Dasari, M. A.; Kiatsimkul, P.-P.; Sutterlin, W. R.; Suppes, G. J. Low-pressure hydrogenolysis of glycerol to propylene glycol Applied Catalysis, A: General, 281(1-2), p. 225 (2005).
U.S. Pat. No. 7,663,004 to Suppes et al., discloses a process for converting glycerin into lower alcohols having boiling points less than 200° C., at high yields. The process involves the conversion of natural glycerin to PG through an acetol intermediate at temperatures from 150° C. to 250° C., at a pressure ranging from 1 to 25 bar (14.5 to 363 psi), and preferably from 5 to 8 bar (72.5 to 116 psi), over a Pd, Ni, Rh, Zn, Cu, or Cr catalyst. The reaction occurs in the presence or absence of hydrogen, with the hydrogen provided by an external source. The glycerin is reacted in solution containing 50% or less by weight water, and preferably only 5% to 15% water by weight.
Regardless of the above, there remains a need for more cost-effective catalysts and methods for reacting complex and higher concentrations of carbohydrate feedstocks (e.g., polysaccharides, oligosaccharides, disaccharides, sugars, sugar alcohols, sugar degradation products, etc.), which are susceptible to thermal degradation at temperatures compatible with deoxygenation reactions, to the desired lower molecular weight oxygenated compounds, such alcohols, ketones, aldehydes, cyclic ethers, carboxylic acids and other polyols. To be cost effective, the catalysts employed must provide effective conversion to the desired compounds at higher yields and without significant saturation into alkanes.